A gas turbine engine generally includes a fan and a core arranged in flow communication with one another. Additionally, the core of the gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, airflow is provided from the fan to an inlet of the compressor section where one or more compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gases through the turbine section drives the compressor section and is then routed through the exhaust section, e.g., to atmosphere. In particular configurations, the turbine section is mechanically coupled to the compressor section by a shaft extending along an axial direction of the gas turbine engine.
The fan includes a plurality of blades having a radius larger than the core of the gas turbine engine. The fan and plurality of blades may also be mechanically coupled to the shaft such that they rotate along with the turbine. In certain configurations, the fan may be mechanically coupled to the shaft through a gear box, such that the fan can have a different rotational speed than the turbine shaft. A rotatable hub can be provided, covering at least a portion of the fan and rotating along with the fan. Rotation of the plurality of blades generates thrust for the gas turbine engine and provides airflow to the compressor section of the core. Additionally, a plurality outlet guide vanes can direct airflow from the blades to, e.g., reduce noise generated by the gas turbine engine and enhance performance of the gas turbine engine. Similar fans also may be provided for other propulsion devices.
For at least some propulsion devices, the fan is a variable pitch fan. It is desirable to vary the pitch of the fan blades by rotating each blade about respective pitch axes to further increase performance of the propulsion device. For example, a primary reason for changing blade pitch is to adjust the blade's angle of attack for optimal performance based on the present air speed of the aircraft and power level of the engine. In addition, the pitch of fan blades may be used to reverse the airflow through the fan, thus providing reverse thrust to aerodynamically brake a landing aircraft.
Generally, the pitch of the fan blades varies between a number of pitch positions such that the fan blades traverse a range of pitches. A certain pitch range may be required to accommodate the various pitch positions associated with different phases of flight and/or optimal performance of the gas turbine engine. However, the pitch range often is restricted by design parameters or considerations such as a solidity of the fan blades and the configuration of various components of the fan, such as counterweights, trunnion mechanisms, and pitch change actuator assemblies.
Accordingly, a variable pitch fan for a propulsion device having features to enable a larger pitch range with optimal design parameters would be desirable. In particular, a variable pitch fan having a plurality of fan blades where a pitch of the fan blades may be varied over an increased pitch range and having an increased solidity in a root region of the fan blades would be beneficial. A variable pitch fan having a plurality of fan blades where a pitch of the fan blades may be varied over an increased pitch range and having a decreased fan hub radius ratio and/or a decreased fan pressure ratio also would be advantageous.